Effective delivery to a patient is a critical aspect of any successful drug therapy. Various routes of delivery exist, and each has its own advantages and disadvantages. Oral drug delivery of pills, capsules, elixirs, and the like is perhaps the most convenient method, but many drugs are degraded in the digestive tract before they can be absorbed. Subcutaneous injection is frequently an effective route for systemic drug delivery, including the delivery of proteins, but enjoys a low patient acceptance. Since injection of drugs, such as insulin, one or more times a day can frequently be a source of poor patient compliance, a variety of alternative routes of administration have also been developed, including transdermal, intranasal, intrarectal, intravaginal, and pulmonary delivery.
Of particular interest, pulmonary drug delivery relies on inhalation of an active agent formulation by the patient so that active drug within the dispersion can reach the distal (alveolar) regions of the lung. This may be accomplished using a patient driven device where it is the inspiratory flow that aerosolizes the active agent formulation or using a drug dispersion or aerosol device that uses a compressed gas or propellant to aerosolize and deliver the active agent formulation.
It has been found that certain drugs are readily absorbed through the alveolar region directly into blood circulation. Pulmonary delivery is particularly promising for the delivery of proteins and polypeptides which are difficult to deliver by other routes of administration. Such pulmonary delivery is effective both for systemic delivery and for localized delivery to treat diseases of the lungs.
Elliot et al, Aust. Paediatr. J. (1987)23:293-297 described the nebulized delivery of semi-synthetic human insulin to the respiratory tracts of six diabetic children and determined that it was possible to control diabetes in these children, although the efficiency of absorption was low (20-25%) as compared to subcutaneous delivery. Laube et al., U.S. Pat. No. 5,320,094, noting Elliot and a number of other studies, stressed that although insulin had been delivered to the lung, none of the patients had responded to the pulmonary insulin therapy sufficient for lowering of blood glucose levels to within a normal range. Laube et al. hypothesized that this problem resulted from the loss of drug in the delivery system and/or in the oropharynx as a result of the method of delivery and that the maximization of deposition within the lungs should improve glucose control in the blood. In order to achieve maximum delivery, Laube et al controlled the inspiratory flow rate at the time of aerosol inhalation at flow rates of less than 30 liters/minute and, preferably about 17 liters/minute. The delivery system included a medication chamber for receiving the insulin, an outlet aperture through which the insulin was withdrawn, and a flow rate limiting aperture to control the inspiratory flow rate.
Commonly assigned U.S. Patent Application No. 60/078,212 tested the above hypothesis and noted that pulmonary delivery of insulin at less than 17 liters per minute provided for increased blood levels of insulin in a shorter time period than higher inspiratory flow rates.
Rubsamen et al, U.S. Pat. Nos. 5,364,838 and 5,672,581 describe the delivery of a measured amount of aerosolized insulin. The insulin is automatically released into the inspiratory flow path in response to information obtained from determining the inspiratory flow rate and inspiratory volume of a patient. A monitoring device continually sends information to a microprocessor, and when the microprocessor determines that an optimal point in the respiratory cycle is reached, the microprocessor actuates the opening of a valve allowing release of insulin. The inspiratory flow rate is in the range of from about 0.1 to 2.0 liters/second and the volume is in the range of from about 0.1 to 0.8 liters.
WO 97/40819 describes slow inspiratory flow rates as being key to increased drug delivery and deposition of drugs delivered via the pulmonary route. In order to obtain the target flow rates (15-60 liters per minute), the device resistance was designed to be within the 0.12 to 0.21 (cm H2O)2. EPO 692990 B1 describes deagglomerators for dry powder inhalers and notes that it is desirable to reduce the airflow rate dependence of the delivered dose and/or respirable fraction of an inhaled powder aerosol. The deagglomerators respond to increasing flow rates to vary the geometry of a channel through which powder laden air passes resulting in a lesser pressure drop increase than would be seen in the absence of the variable geometry and that provide for more effective deagglomeration over a range of flow rates.
We have now determined that, in order to effectively deliver an active agent via the pulmonary route in a comfortable and reproducible manner, it is desirable to maintain a low initial flow rate followed by a period of higher flow.